| Pea (Pisum sativum L.) is a poverty saving crop, traditionally cultivated in under-developed areas with mountainous margin farmland in China. It is almost an omnipotent crop for its early maturity, wide environmental adaptability and multi-purpose; also it can grow well in both rained and irrigated farmland as grain, vegetable and fodder crops. The genetic diversity of pea has been accumulated during its distribution and release from rainfed agriculture to irrigated system, also from high upland to plain area from ancient times. But, relatively short of genetic diversity researches in China for effective use of pea genetic resources can not integrate with the traditional breeding. At meantime, the international and domestic markets demand better quality and professional functioning pea products, which led more and severe requests from national and provincial breeding programs for better diversified varieties to meet market needs. However, genetic diversity is the key to the success of breeding program, that request breeding programs for better understanding of pea genetic resources in order to break the bottleneck on existed narrow genetic background of commercial varieties. Creation of new genetic resources with high quality, professional purposes and multi-resistance ability to diseases is the method to break the bottleneck, for which we invited 624 geographic core collections of cultivated pea genetic resources from all over the world for genetic diversity analysis based on morphological characters to get better and detailed knowledge for effective screening of pea breeding parents. The main results for this morphological genetic diversity analysis are reported as following:1,The diversity index of the 20 morphological characters based on 624 accessions is 1.369 on average, which means high genetic diversity level existed in the tested samples. The 7 qualitative characters possess a low genetic diversity (0.896) on average. While, the diversity index of the 13 quantitative characters is 1.624, which is 81.25% higher than that of qualitative characters. The highest value (2.028) of genetic diversity index is appeared in seed weight per plant; the lowest value (0.207) occurred in leaf type.2,The average genetic diversity of accession groups from north part of China, south part of China, and five continents, is 1.008, which probably means rich diversity in each group of genetic resources. The genetic diversity index (1.137) of foreign genetic resources (201 accessions) is 0.170 greater than that (0.967) of domestic genetic resources (423 accessions). The genetic diversity index (1.024) of north China group (270 accessions) is 0.120 greater than that (0.904) of south China group (153 accessions), which means better genetic diversity in north part of China. For the five continents, the highest genetic diversity index appeared in European group (46 accessions, 1.262), followed by Asian group (56 accessions, 1.258), African group (53 accessions, 1.171), unknown group (10 accessions, 1.089), Oceania group (25 accessions, 1.020) and American group (11 accessions, 1.020).3,Based on Structure 2.2 software, 4 morphological clusters were identified from the 624 candidate genetic resources, which associated well with their geographical origins. The genetic resources (165 accessions) from the five northwestern provinces of China were clustered in Cluster 3 and Cluster 2, the genetic resources (73 accessions) from 3 central provinces of China were clustered in Cluster 1 and Cluster 3, and the genetic resources (32 accessions) from the 2 northeastern provinces of China were clustered in Cluster 1. On Chinese genetic resources (153 accessions) from south part of China, the genetic resources (101 accessions) from 3 southwestern provinces were clustered in Cluster 1 and in Cluster 3. While, the genetic resources (34 accessions) from the 2 eastern provinces of China mainly clustered in Cluster 3 and Cluster 1. The genetic resources (18 accessions) from the 3 central provinces and 1 southern province were dispersed in clusters, with non-obvious geographical correlation. Except the 13 accessions in Cluster 1, other foreign genetic resources were all clustered in Cluster 4. The mean genetic distance among the 4 clusters is 0.1639 and the mean genetic distance among accessions within each cluster is 0.5372. The value of genetic distance among clusters and accessions in each cluster is relatively coincided with their geographic origins.4,The principal component analysis (PCA) based on the 20 morphological characters showed 86.71% coverage for the 12 major principal components. That means the 12 major principal components covered the majority of the information that all the 20 components provided.
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